Electrical coil and method of manufacturing it



C. A. PURDY ELECTRICAL COIL AND METHOD OF MANUFACTURING IT March 4,1930.

Filed Oct. 19, 1926 v //7 l/ema/ 6/7esfe/ A. Pa/d Patented Mar. 4, 1930UNITED STATES PATENT OFFICE CHESTER ARTHUR PURDY, OF OAK PARK, ILLINOIS,ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y.,A CORPORATION OF NEW YORK ELECTRICAL COIL AND METHOD OF MANUFACTURING ITApplication i i-led October 19, 1926. Serial No. 142,561.

This invention relates to electrical coils and a method of manufacturingthem, and more particularly to inductance coils having toroidal typecores and a method of manufacturing them.

One type of inductance toroidal core coils which is used in connectionwith telephone lines to which this invention is particularly applicablecomprises two coils having a large number of turns of fine wire woundthereon, the coils being assembled on two substantially identicalarcuate sections of a ring core com posed of magnetic material, whichhave heretofore been permanently clamped together with non-magneticclamping elements. The manufacture of an inductance coil of this typewith predetermined electrical properties is a comparatively difiicultand expensive procedure in that in the winding of the coils thereof anexcess number of turns of wire are frequently wound thereon which in thesubsequent inductance adjustment of the coil requires the removal of alarge portion thereof and in some cases the addition of turns of wiresto provide a coil of predetermined electrical characteristics.

The objects of this invention are to provide an improved type ofelectrical coil and a method of manufacturing them to a definiteinductance in a simple, inexpensive and expe-' ditious manner.

In accordance with the objects of this invention as practiced inconnection with the manufacture of toroidal core inductance coils of thetype hereinbefore described the two sections of the ring core with theirrespective coils mounted thereon are assembled with a non-magneticcementing material applied in plastic form between the adjacent oppositeends. The thus assembled coils and the respective core sections aremounted upon an adjustable clamping fixture where the core sections areeach individually adapted to be moved toward or from each other in adirection at substantially right angles to the opposed cemented endswhereby the air gap may be adjusted until a predetermined definiteinductance is obtained as indicated by a suitable bridge or test circuitconnected to the windings of the coil. With this adjustment of the airgap it isnot necessary to remove or add any turns of wire to the coilsections. After obtaining the desired inductance the coil isdisconnected from the bridge circuit and the plastic cement is allowedto harden to provide a permanent air gap whereupon the coil is removedfrom the clamping fixture and is then ready to be incased or mountedwithout further clamping means being applied to .retain the coresections in assembled relation.

Other objects and advantages of this invention will more fully appearfrom the accompanying detailed descriptiontaken in connection with theaccompanying drawing which illustrates one embodiment thereof, in whichFig. 1 is a perspective view of a completed inductance toroidal corecoil embodying the features of this invention before it is incased ormounted;

Fig. 2 is a side elevation of an assembling fixture used in practicingthe method of manufacturing the coil illustrated in Fig. 1;

Fig. 3 is a plan View thereof with a coil in position thereon;

Fig. 4 is an end view thereof, and

Fig. 5 is a schematic diagram of a coil connectedto a bridge circuit forindicating when the magnetic gap of the coil has been adjusted toprovide a definite inductance.

An inductance toroidal core coil embodying the features of thisinvention may be manufactured according to the following method.Referring to the drawings, particularly Fig. 1 which illustrates acompleted coil before being incased or mounted,

the numerals 10 and 11 indicate semi-toroids,

forming the core of the coil, which may be composed of any suitablemagnetic material. In practice, it has been found desirable to form thecore first in the form of a continuous ring from finely divided ironparticles, the individual particles of which are coated with a thininsulating film which are then formed under high pressure into a ring ina well known manner. The ring thus formed after being coated with a thininsulating film is suitably broken into two substantially identicalcircumferential sections or semi-toroids 10 and 11. Upon each of thesemi-toroids equi-distant the ends thereof is mounted a spool 12provided with heads 13 at opposite ends and having a large number ofturns of fine Wire 14 wound thereon between the heads, the spools beingprovided with apertures 17 adapted to receive the core sections. Thebroken ends of the core sections 10 and 11 are then treated with asuitable non-magnetic plastic cement 18 which hardens slowly at roomtemperatures. In case it is desired to hasten the hardening the coil maybe placed in a heated oven.

According to one embodiment of the invention, a cement having a lowcoefficient of expansion under temperature change after hardening isemployed. A cement having these qualities which has been found to beparticularly suited for the purpose herein described is known under thetrade name of Ambroid.

The two core sections thus treated with the cement 18 and supporting thespools 12 of wire are mounted upon an adjustable clamping fixture 19(Figs. 2, 3 and 4) with the original broken ends in adjacentrelationship and spaced apart by the cement 18 to form a non-magneticgap for breaking the continusheet material such as brass.

ity of the magnetic circuit. The fixture 19 will now be described.

The fixture 19 comprises a pair of similarly shaped diametricallydisposed arms 20 extending vertically form a horizontally disposedcommon supporting base 21, the whole being formed integrally fromnon-magnetic The upper ends ofthe arms 20 are each provided with a pairof inwardly extending arms 22 formed at right angles thereto. Formedupon each of the arms 22 is a pair of vertically extending .jaws 23which are suitably spaced from each other and set at an angle withrespect to the arms 22 so that they snugly engage the outer and innercurved vertical surfaces of the arcuate sections of the ring core, asclearly indicated in Fig. 3, u on the coil sections 4 being associatedtherewith, the lower surfaces of the core sections resting upon upperhorizontal edge surfaces 26 of the arms 22 intermediate each pair ofjaws 23. The arms 20 and base 21 are tensioned in the forming of thefixture so that the arms 20 are normally urged apart for a suitabledistance, as clearly shown in Fig. 2. To provide positive motion betweenthe arms 20 to bring them closer together a rod 27 extends from one armto the other intermediate the arms 22, as viewed in Fig. 3, and throughopenings provided there in. One end of the rod 27 is threaded into a nutor lug 28'preferably soldered to the associated arm 20, while theopposite end' of the rod is equipped with a thumb piece 29. It will beevident that the normal tensionprovided in the fixture as hereinbe'forementioned and a manipulation of the threaded rod 27 provides meanswhereby the arms 22 may be adjusted horizontally in either direction tovary the space between the opposed pairs of jaws 23 provided. upon theinner ends of the arms 22.

Fig. 5 illustrates in diagrammatic form an electrical Vheatstone bridgecircuit which is used in the inductance adjustment of the coilsmanufactured in accordance with the herein described method. In thisdiagram A and B represent the usual fixed ratio arms comprisingresistances and 36, C a variable arm in-- cluding an adjustableresistance 37 and an adjustable inductance resistance 38, and D theunknown resistance arm of the bridge circuit comprising the coil to beadjusted to a predetermined inductance. An electromotive force supplysource 39 of audio fre quency alternating current is connected to thepoints 40 and 41, while the circuit between the points 42 and 43includes a telephone receiver 44 which is used in a well known manner toindicate to the operator when the bridge circuit is balanced.

The method of integrally uniting the core sections 10 and 11 with theirrespective spools or coils 12 mounted thereonand adjusting thenon-magnetic gap between the opposite core sections until the desiredinductance of the coils is obtained is as follows:

The broken ends of the core sections 10 and 11, as hereinbeforedescribed, are treated with the plastic non-magnetic cement 18 after themounting of the coil thereon. Thereafter the core sections are placed bythe operator upon the two arms 22 of the fixture 19 which normallyassume the position shown in Fig. 2, with the inner and outer curvedvertical surfaces ofthc core sections'lying between the jaws 23 of thearms 22 and their lower sur faces resting upon the upper horizontal edgesurfaces 26 of the arms 22, as clearly shown in Figs. 3 and 4. The twocoils 12 carried by the core sections are then connected to the bridgecircuit to form the unknown arm D thereof, as hereinbefore' describedand shown in Fig. 5, with the inner and outer ends 45 and 46,respectively, of the wires forming the two coils connected together andthe outer and inner ends 47 and 48, respectively, thereof seriallyconnected to the arm D. Before the adjusting operation takes lace it isto be understood that the variab e arm C of the bridge circuit has beenset by ad'usting the inductance resistance 38 for the esired coilinductance and that the adjustable resistance 37 has also been set tocorrespond to the resistance of the coil under ad ustment. The coresections 10 and 11 are then moved toward each other in the mannerhereinbefore described by turning the rod 27, the space between the coresections being bridged by the plastic cement 18. \Vhile thus-varying thenon-magnetic gap the operator is holding the receiver 44 to his ear andupon the inductance in the unknown arm D equalling the inductance in thearm C. which as hereinbefore ill mages described has been set for theinductance desired'in the coil under adjustment, the high frequency humof the alternating current source 39 across the points 40 and 41 willnot be heard by the operator, since no current will flow between thepoints 42 and 43 when the bridge circuit is in balance. This indicatesto the operator that the inductance adjustment of the coil is completed,the coil ends 47 and 48 are then disconnected from the bridge circuitand the assembled adjusted coil still clamped to the fixture is setaside to permit the cement 18 to harden at room ten'iperature-or it maybe placed in a heated oven to accelerate the hardening thereof. The coilis then released from the fixture 19 and is ready to be incased ormounted without further clamping means being applied to retain the coresections in assembled relation.

What is claimed is: s i

l. The method of manufacturing electrical coils which consists inplacing a winding on a divided core, positioning a plastic nonmagneticmaterial between the ends of the core which provides an air gap betweenthe core sections, and adjusting said air gap with the non-magneticmaterial in a plastic state until predetermined electrical propertiesare obtained.

2. The method of manufacturing electrical coils which consists'informing a core, dividing the core into a plurality of substantiallyidentical sections, placing windings thereon in sections, assembling thecore sections in spaced relation with a plastic non-magnetic materialbridging the space therebetween, and then varying the space between thecore sections until a definite predetermined effect is obtained in thecoil.

3. The method of manufacturing electrical coils which consists informing a core of magnetic material, dividing the core into a pluralityof sections, placing windings thereon in sections, treating a surface ofone core section with a plastic non-magnetic material, assembling thecore sections in spaced relation with a plastic non-magnetic material,bridging the space between the core sections, connecting the windingswith an electrical test circuit, and then varying the space be tween thecore sections until a definite predetermined efiect is obtained in thecoil as indicated by the test circuit.

4. The method of manufacturing electrical coils, which consists informing a core, fracturing the core to provide a plurality of secionshaving opposed irregular surfaces, placi n g a winding on the core,positioning a plas tic non-magnetic material between the irregular coresurfaces which provides an air gap between the core sections, andadjusting said air gap until predetermined electrical properties areobtained.

5. The method of manufacturing electrical coils, which consists inplacing a winding on a divided core, positioning a cementitiousnon-magnetic material between the ends of the core which provides an airgap between he core sections, and adjusting said air gap before thecementitious material becomes ef fective until predetermined electricalprop ertics are obtained.

6. The method of manufacturing electrical coils, which consists informing an endless core, dividing the core into sections, placingwindings thereon in sections, assembling the 0110 sections in spacedrelation to provide an air gap thercbetween, bridging the air gap by aplastic nonmagnetic material, and then varyin the air gap between thecore sections until a definite predetermined effect is obtained in thecoil.

7. The method of manufacturing electrical coils, which consists informing an annular core, dividing the core into a plurality of sectionsplacing windings thereon in sections, tlF'fitll'lbllllg the coresections in spaced relation to provide an air gap therebetwcen, bridgingthe air gap by a plastic non-mag nctic material, and then varying theair gap between the core sections with the non magnetic material in aplastic state until a delinite predetermined effect is obtained in thecoil.

8. An inductancecoil having a core formed of separated sections, and aquantity of non magnetic cementing. material between the sectionspermitting adjustment of the air gap between the sections and uponsolidification integrally uniting the sections.

9. An inductance coil having a core formed of a plurality ofsubstantially identical semitoroids spaced apart at diametricallyopposite points, and a non-magnetic cementing material in the spacebetween the semi-toroids to allow for adjustment of the air gap betweenthe semi-toroids and upon its solidification integrally uniting thesemi-toroids.

10. In an inductance coil having a core formed of magnetic materialseparated at opposite points, a cementitious non-magnetic spacerallowing initial relative adjustment of the points to vary the air gapand integrally uniting the points.

In witness whereof, I hereunto subscribe my name this 4th day ofOctober, A. D. 1926.

CHESTER ARTHUR PURDY.

